Opto-electronic integrated circuits (OEICS) may incorporate both electronic circuits and optical devices, such as integrated waveguides, modulators, switches, and detectors. The optical devices may be used for, e.g., optical clock distribution, intra-chip optical signaling, and chip-to-chip communication Both the electronic circuits and optical devices may be produced on silicon using complementary metal-oxide semiconductor (CMOS) fabrication techniques.
Light utilized by optical devices in an OEIC may be introduced into the chip by an external source, such as a vertical cavity surface emitting laser (VCSEL) or an optical fiber. The light from the external source may have a relatively large mode compared to that of the on-chip waveguides. The differences in mode size may present difficulties in efficiently coupling the relatively large mode off-chip light source to a small waveguide on the chip.